Cell biology of the plant–powdery mildew interaction

doi:10.1016/j.pbi.2011.08.002

Current Opinion in Plant Biology

Volume 14, Issue 6, December 2011, Pages 738-746

https://doi.org/10.1016/j.pbi.2011.08.002 Get rights and content

Powdery mildew fungi represent a paradigm for obligate biotrophic parasites, which only propagate in long-lasting intimate interactions with living host cells. These highly specialized phytopathogens induce re-organization of host cell architecture and physiology for their own demands. This probably includes the corruption of basal host cellular functions for successful fungal pathogenesis. Recent studies revealed secretory processes by both interaction partners as key incidents of the combat at the plant–fungus interface. The analysis of cellular events during plant–powdery mildew interactions may not only lead to a better understanding of plant pathological features, but may also foster novel discoveries in the area of plant cell biology.

Highlights

► Plant–powdery mildew interactions are well suited for cell biological analyses. ► Cell-autonomous plant defence responses enable single cell studies. ► MLO proteins are crucial for successful entry of powdery mildews into host cells. ► Secretory processes from both organisms occur at the plant–fungus interface. ► Arabidopsis RPW8 is the first plant protein found at the extrahaustorial membrane.

Introduction

Powdery mildew is a widespread disease of many monocotyledonous and dicotyledonous plants that is caused by obligate biotrophic Ascomycetes of the order Erysiphales. Traditionally, the main thrust of powdery mildew research was devoted to disease resistance, especially in cereals such as wheat and barley. Accordingly, extensive genetic analyses during previous decades revealed major resistance genes that typically confer isolate-specific immunity in these species [1]. More recently, other host species, such as the dicotyledonous reference species Arabidopsis thaliana [2], and different aspects of this plant–pathogen interaction, such as fungal pathogenesis and the establishment of compatibility [3, 4], gained increasing attention. This also applies to cell biological examination of plant–powdery mildew encounters, which are ideally suited for microscopic studies since the fungal pathogen exclusively colonizes the epidermal cell layer and thus host–pathogen contact sites remain readily accessible for microscopy (Figure 1). Moreover, owing to cell-autonomous nature of plant defence against powdery mildew invasion [5], the interaction is well suited for single cell analyses [6]. The obligate biotrophic pathogen accommodates dedicated infection structures, haustoria (Figure 2), inside colonized host cells. The associated perturbation of plant cellular structure and the dynamic responses of the host cell to this assault [7] bring up highly interesting cell biological questions. Consequently, during the past few years several excellent papers were published that highlight various cell biological aspects of the plant–powdery mildew interaction.

Section snippets

Early events: Fungal spore germination and appressorium formation

The asexual powdery mildew life cycle commences with the landing of conidiospores on the plant surface. Proteomic analyses of conidia from the barley pathogen Blumeria graminis f.sp. hordei (Bgh) revealed numerous proteins with functions in carbohydrate, lipid or protein metabolism, indicating that resting conidia are prepared for the catabolism of storage compounds as well as protein biosynthesis and folding [8, 9]. Following spore germination, appressoria develop at the sites where fungal

The next step: The switch from surface growth to invasive fungal pathogenesis

Probably the most crucial step in powdery mildew pathogenesis is the successful invasion of the first epidermal cell. Effective host cell penetration in barley [12], Arabidopsis [13], tomato [14] and pea [15] requires presence of wild type variants of plant Mildew Locus O (MLO) genes, indicating a common molecular mechanism of powdery mildew pathogenesis in monocotyledonous and dicotyledonous plants. Recessively inherited loss-of-function mlo alleles mediate broad-spectrum powdery mildew

The fungal haustorium

Following successful host cell invasion, the accommodation of haustoria inside plant cells represents the next major step during powdery mildew pathogenesis. Haustoria remain separated from the plant cytoplasm since they are covered by the extrahaustorial membrane, a host plasma membrane derivative that tightly surrounds invading fungal haustoria (Figure 2). The extrahaustorial membrane differs markedly in its molecular composition from the conventional host plasmalemma and was previously found

Host cellular rearrangements during powdery mildew infection

The host cell architecture greatly changes for accommodation of the haustorial complex. This involves dynamic rearrangements of endomembrane compartments and the cytoskeleton (Figure 1) that are reminiscent of cellular reorganization events following a mechanical stimulus [49]. Plant RHO-like GTPases (RAC/ROPs) are considered major players in plant cytoskeleton organization. The barley RAC/ROP small GTPase RACB is a susceptibility factor required for the establishment of haustoria of Bgh in

Later stages of powdery mildew pathogenesis

Post-penetration colonization involves the suppression of host cell death. ENHANCED DISEASE RESISTANCE 1 (EDR1) is a conserved protein kinase required for full susceptibility to powdery mildew in Arabidopsis. Loss of EDR1 leads to salicylic acid signalling-dependent and late cell death-associated post-penetration resistance to G. cichoracearum [54]. Enhanced disease resistance of edr1 mutants is not specific for powdery mildew [54], but correlates with an increased transcriptional response to

Conclusions

Novel discoveries in plant cell biology have been made on the basis of the powdery mildew–plant system owing to the highly localized host responses upon infection by these obligate biotrophic phytopathogens. The induced site-specific host responses enable in some cases the detection of phenotypes that are otherwise masked by genetic redundancy. An example of this concept is the altered state of endoreduplication in the myb3r4 single mutant [60^••], whereas double mutants were required to observe

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

• of special interest
•• of outstanding interest

Acknowledgements

We thank Wenming Wang, Shunyuan Xiao, Hans Thordal-Christensen, Ulla Neumann, Caroline Hoefle, Ruth Eichmann, Maya Ostertag, and Qianli An for providing unpublished micrographs. Work in the lab of RP is supported by grants from the Max-Planck society and the Deutsche Forschungsgemeinschaft (DFG; SFB670). Work in the lab or RH is supported by the German Research Foundation and the Federal Ministry of Research and Education.

References (69)

R. Hückelhoven
Powdery mildew susceptibility and biotrophic infection strategies
Fems Microbiol Lett
(2005)
V. Lipka et al.
Dynamic cellular responses in plant-microbe interactions
Curr Opin Plant Biol
(2005)
L.V. Bindschedler et al.
In planta proteomics and proteogenomics of the biotrophic barley fungal pathogen Blumeria graminis f. sp hordei
Mol Cell Proteomics
(2009)
R. Büschges et al.
The barley Mlo gene: a novel control element of plant pathogen resistance
Cell
(1997)
A. Devoto et al.
Topology, subcellular localization, and sequence diversity of the Mlo family in plants
J Biol Chem
(1999)
B. He et al.
The exocyst complex in polarized exocytosis
Curr Opin Cell Biol
(2009)
T. Pecenkova et al.
The role for the exocyst complex subunits Exo70B2 and Exo70H1 in the plant-pathogen interaction
J Exp Bot
(2011)
I.P. Pathuri et al.
Constitutively activated barley ROPs modulate epidermal cell size, defense reactions and interactions with fungal leaf pathogens
Plant Cell Rep
(2008)
L.Q. Chen et al.
Sugar transporters for intercellular exchange and nutrition of pathogens
Nature
(2010)
D. Nowara et al.
HIGS: Host-Induced Gene Silencing in the obligate biotrophic fungal pathogen Blumeria graminis
Plant Cell
(2010)

J.H. Jørgensen

Genetics of powdery mildew resistance in barley

Crit Rev Plant Sci

(1994)

C. Micali et al.

The powdery mildew disease of Arabidopsis: a paradigm for the interaction between plants and biotrophic fungi

The Arabidopsis Book

(2008)

R.J. O’Connell et al.

Tête à tête inside a plant cell: establishing compatibility between plants and biotrophic fungi and oomycetes

New Phytol

(2006)

K. Shirasu et al.

Cell-autonomous complementation of mlo resistance using a biolistic transient expression system

Plant J

(1999)

R. Panstruga

A golden shot: how ballistic single cell transformation boosts the molecular analysis of cereal-mildew interactions

Mol Plant Pathol

(2004)

S. Noir et al.

A proteomic analysis of powdery mildew (Blumeria graminis f.sp. hordei) conidiospores

Mol Plant Pathol

(2009)

J. Feng et al.

Analysis of a Blumeria graminis-secreted lipase reveals the importance of host epicuticular wax components for fungal adhesion and development

Mol Plant-Microbe Interact

(2009)

A. Hansjakob et al.

Very-long-chain aldehydes promote in vitro prepenetration processes of Blumeria graminis in a dose- and chain length-dependent manner

New Phytol

(2010)

C. Consonni et al.

Conserved requirement for a plant host cell protein in powdery mildew pathogenesis

Nat Genet

(2006)

Y.L. Bai et al.

Naturally occurring broad-spectrum powdery mildew resistance in a central American tomato accession is caused by loss of Mlo function

Mol Plant-Microbe Interact

(2008)

Humphry M, Reinstädler A, Ivanov S, Bisseling T, Panstruga R: Durable broad-spectrum powdery mildew resistance in pea...

M.C. Kim et al.

Calmodulin interacts with MLO protein to regulate defence against mildew in barley

Nature

(2002)

R.A. Bhat et al.

Recruitment and interaction dynamics of plant penetration resistance components in a plasma membrane microdomain

Proc Natl Acad Sci USA

(2005)

M. Humphry et al.

A regulon conserved in monocot and dicot plants defines a functional module in antifungal plant immunity

Proc Natl Acad Sci USA

(2010)

M. Humphry et al.

mlo-based powdery mildew immunity: silver bullet or simply non-host resistance?

Mol Plant Pathol

(2006)

N.C. Collins et al.

SNARE-protein-mediated disease resistance at the plant cell wall

Nature

(2003)

C. Consonni et al.

Tryptophan-derived metabolites are required for antifungal defense in the Arabidopsis mlo2 mutant

Plant Physiol

(2010)

P. Bednarek et al.

A glucosinolate metabolism pathway in living plant cells mediates broad-spectrum antifungal defense

Science

(2009)

Z.Y. Chen et al.

Two seven-transmembrane domain MILDEW RESISTANCE LOCUS O proteins cofunction in Arabidopsis root thigmomorphogenesis

Plant Cell

(2009)

S.A. Kessler et al.

Conserved molecular components for pollen tube reception and fungal invasion

Science

(2010)

M. Kwaaitaal et al.

Combined Bimolecular Fluorescence Complementation and Förster Resonance Energy Transfer reveals ternary SNARE complex formation in living plant cells

Plant Physiol

(2010)

C. Kwon et al.

Co-option of a default secretory pathway for plant immune responses

Nature

(2008)

S. Pajonk et al.

Activity determinants and functional specialization of Arabidopsis PEN1 syntaxin in innate immunity

J Biol Chem

(2008)

H. Böhlenius et al.

The multivesicular body-localized GTPase ARFA1b/1c is important for callose deposition and ROR2 syntaxin-dependent preinvasive basal defense in barley

Plant Cell

(2010)

Cited by (126)

Is CRISPR/Cas9-based multi-trait enhancement of wheat forthcoming?
2024, Plant Science
Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) technologies have been implemented in recent years in the genome editing of eukaryotes, including plants. The original system of knocking out a single gene by causing a double-strand break (DSB), followed by non-homologous end joining (NHEJ) or Homology-directed repair (HDR) has undergone many adaptations. These adaptations include employing CRISPR/Cas9 to upregulate gene expression or to cause specific small changes to the DNA sequence of the gene-of-interest. In plants, multiplexing, i.e., inducing multiple changes by CRISPR/Cas9, is extremely relevant due to the redundancy of many plant genes, and the time- and labor-consuming generation of stable transgenic plant lines via crossing. Here we discuss relevant examples of various traits, such as yield, biofortification, gluten content, abiotic stress tolerance, and biotic stress resistance, which have been successfully manipulated using CRISPR/Cas9 in plants. While existing studies have primarily focused on proving the impact of CRISPR/Cas9 on a single trait, there is a growing interest among researchers in creating a multi-stress tolerant wheat cultivar ‘super wheat’, to commercially and sustainably enhance wheat yields under climate change. Due to the complexity of the technical difficulties in generating multi-target CRISPR/Cas9 lines and of the interactions between stress responses, we propose enhancing already commercial local landraces with higher yield traits along with stress tolerances specific to the respective localities, instead of generating a general ‘super wheat’. We hope this will serve as the sustainable solution to commercially enhancing crop yields under both stable and challenging environmental conditions.
Evaluation of host resistance and susceptibility to Podosphaera aphanis NWAU1 infection in 19 strawberry varieties
2023, Scientia Horticulturae
Strawberry powdery mildew, caused by the obligate biotrophic fungus Podosphaera aphanis, is one of the most devastating diseases in strawberry, resulting in severe reduction in fruit yield and quality. Exploring and utilizing powdery mildew-resistant strawberries is an important disease management strategy. The present study evaluated the resistance of 19 strawberry varieties to Podosphaera aphanis NWAU1 (Pa. NWAU1) based on disease index. We have comprehensively investigated the different cytological and physiological responses of different resistant strawberries. Compared with highly susceptible (HS) strawberries 'Benihoppe' and 'Tianxianzui', the moderately resistant (MR) strawberries 'Heilongjiang' and 'Yellow Wonder' exhibited higher levels of callose and H₂O₂ accumulation after inoculation with Pa. NWAU1. The activities of SOD, POD, GPX, and the GSH level in HS strawberries were increased after inoculation with Pa. NWAU1. The SA and JA levels in resistant strawberries were almost similar. However, the ACC level varied in HS and MR strawberries. Our results indicate that increased levels of callose, H₂O₂ and ACC resulted in resistance to Pa. NWAU1 in MR strawberries. The higher antioxidant enzyme activities may contribute to the sensitivity to Pa. NWAU1 in HS strawberries. Our study provides a reliable and comprehensive method for evaluating and understanding potential defense responses to powdery mildew resistance in different strawberries.
Genome-wide characterization and expression analysis of the MLO gene family sheds light on powdery mildew resistance in Lagenaria siceraria
2023, Heliyon
MLO (mildew locus O) genes play a vital role in plant disease defense system, especially powdery mildew (PM). Lagenaria siceraria is a distinct Cucurbitaceae crop, and PM is one of the most serious diseases threatening crop production and quality. Although MLOs have been exploited in many Cucurbitaceae species, genome-wide mining of MLO gene family in bottle gourd has not been surveyed yet. Here we identified 16 MLO genes in our recently assembled L. siceraria genome. A total of 343 unique MLO protein sequences from 20 species were characterized and compared to deduce a generally high level of purifying selection and the occurrence of regions related to candidate susceptibility factors in the evolutional divergence. LsMLOs were clustered in six clades containing seven conserved transmembrane domains and 10 clade-specific motifs along with deletion and variation. Three genes (LsMLO3, LsMLO6, and LsMLO13) in clade V showed high sequence identity with orthologues involved in PM susceptibility. The expression pattern of LsMLOs was tissue-specific but not cultivar-specific. Furthermore, it was indicated by qRT-PCR and RNA-seq that LsMLO3 and LsMLO13 were highly upregulated in response to PM stress. Subsequent sequence analysis revealed the structural deletion of LsMLO13 and a single nonsynonymous substitution of LsMLO3 in the PM-resistant genotype. Taken all together, it is speculated that LsMLO13 is likely a major PM susceptibility factor. The results of this study provide new insights into MLO family genes in bottle gourd and find a potential candidate S gene for PM tolerance breeding.
Fine mapping of an adult-plant resistance gene to powdery mildew in soybean cultivar Zhonghuang 24
2022, Crop Journal
Powdery mildew (PM), caused by the fungus Microsphaera diffusa, causes severe yield losses in soybean [Glycine max (L.) Merr.] under suitable environmental conditions. Identifying resistance genes and developing resistant cultivars may prevent soybean PM damage. In this study, analysis of F₁, F_2, and F_8:11 recombinant inbred line (RIL) populations derived from the cross between Zhonghuang 24 (ZH24) and Huaxia 3 (HX3) indicated that adult-plant resistance (APR) to powdery mildew in the soybean cultivar (cv.) ZH24 was controlled by a single dominant locus. A high-density genetic linkage map of the RIL population was used for fine mapping. The APR locus in ZH24 was mapped to a 281-kb genomic region on chromosome 16. Using 283 susceptible plants of another F₂ population, the candidate region was fine-mapped to a 32.8-kb genomic interval flanked by the markers InDel14 and Gm16_428. The interval harbored five genes, including four disease resistance (R)-like genes, according to the Williams 82.a2.v1 reference genome. Quantitative real-time PCR assays of candidate genes revealed that the expression levels of Glyma.16g214300 and Glyma.16g214500 were changed by M. diffusa infection and might be involved in disease defense. Rmd_B13 showed all-stage resistance (ASR) to PM in soybean cv. B13. An allelism test in the F₂ segregating population from the cross of ZH24 × B13 suggested that the APR locus Rmd_ZH24 and the ASR locus Rmd_B13 may be allelic or tightly linked. These results provide a reference marker-assisted selection in breeding programs.
Induced host defense by virulence manipulation of Erysiphe orontii through exogenous application of apoplastic nutrients
2022, Physiological and Molecular Plant Pathology
Citation Excerpt :
E. orontii causes the structural and functional alterations such as induced colonization in host tissues and accumulation of phytoalexins leading to host cell death [26]. The biochemical adaptation of the host included the up-regulated level of salicylic acid and down-regulated level of auxins in the infected tissues, oxidative burst inducing higher level of ROS (reactive oxygen species) and HR (hypersensitive response) to retard the growth of E. orontii [27]. The protocols permitting the rapid quantification of disease caused by E. orontii are either qPCR-based evaluation of fungal biomass, or the fungal condiospores quantification [28,29].
Host apoplastic nutrients might influence the proliferating biotroph, therefore, we analyzed the effect of host apoplastic nutrients on the virulence strategy of E. orontii (a biotroph model). E. orontii was initially treated with the analogs of commonly found apoplastic nutrients in a culture media. The analogs included Cyanoalanine (CAL), Trehalose, H₂O₂, acidic water (0.3% H₃PO₄), NaNO_3, and MgSO₄. After pre-treatment with the analogs of apoplastic nutrients, E. orontii was then inoculated to the host plants. After 5 and 8 days of post-infection (dpi), the virulence of E. orontii was determined through the expression of 20 virulence factor and 7 host defence genes. The expression of AVRk1, Ekal1, Ekal2, Ekal3, Ekal4, Ekal5, Ekal6, Ekal7, Ekal8, Epul5, Epul6, Epul7, Epul8, Epul9, Epul10, Epul11, Epul12, Epul5, Epul17 was determined as a virulence factor and expression of PR1, ERF1, PDF1.2a, PMRs, DMRs, IOS1, MYB3R4 was determined as host defence genes. The results revealed that the tested analogs vigorously affected the phenotypic and genotypic properties of E. orontii and thus its biotrophic virulence strategy. Certainly, the exogenous application of fungal growth-promoting apoplastic nutrients (CAL or TRE) severely reduced the virulence of E. orontii. Contrarily, the stress-inducing apoplastic analogs (H₂O₂ or acidic water) surprisingly increased the virulence of E. orontii. Moreover, the application of NaNO₃ or MgSO₄ decoyed the fungal growth and thus decreasing the E. orontii virulence.
Polarized NORTIA accumulation in response to pollen tube arrival at synergids promotes fertilization
2021, Developmental Cell
Citation Excerpt :
For example, an interesting parallel between powdery mildew infection and PT reception is that in both cases, an MLO protein accumulates at the site of interaction with a tip-growing cell. During powdery mildew infection, active transport of proteins and lipids to penetration site leads to membrane remodeling and establishment of the extrahaustorial membrane (EHM) which separates the plant cytoplasm from the invading fungal hyphae (Hückelhoven and Panstruga, 2011). This specialized membrane is enriched in the anionic phospholipid phosphatidylinositol 4,5 bisphosphate (PI(4,5)P2).
Signal-mediated regulation of protein trafficking is an elegant mechanism for controlling the delivery of molecules to a precise location for critical signaling events that occur over short time frames. During plant reproduction, the FERONIA receptor complex is critical for intercellular communication that leads to gamete delivery; however, the impact of the FERONIA signal transduction cascade on protein trafficking in synergid cells remains unknown. Live imaging of pollen tube reception has revealed that a key outcome of FERONIA signaling is polar accumulation of the MLO protein NORTIA at the filiform apparatus in response to signals from an arriving pollen tube. Artificial delivery of NORTIA to the filiform apparatus is sufficient to bypass the FERONIA signaling pathway and to promote interspecific pollen tube reception. We propose that polar accumulation of NORTIA leads to the production of a secondary booster signal to ensure that pollen tubes burst to deliver the sperm cells for double fertilization.

View all citing articles on Scopus

View full text

Cell biology of the plant–powdery mildew interaction

Highlights

Introduction

Section snippets

Early events: Fungal spore germination and appressorium formation

The next step: The switch from surface growth to invasive fungal pathogenesis

The fungal haustorium

Host cellular rearrangements during powdery mildew infection

Later stages of powdery mildew pathogenesis

Conclusions

References and recommended reading

Acknowledgements

Fems Microbiol Lett

Curr Opin Plant Biol

Mol Cell Proteomics

Cell

J Biol Chem

Curr Opin Cell Biol

J Exp Bot

Plant Cell Rep

Nature

Plant Cell

Genetics of powdery mildew resistance in barley

Crit Rev Plant Sci

The powdery mildew disease of Arabidopsis: a paradigm for the interaction between plants and biotrophic fungi

The Arabidopsis Book

Tête à tête inside a plant cell: establishing compatibility between plants and biotrophic fungi and oomycetes

New Phytol

Cell-autonomous complementation of mlo resistance using a biolistic transient expression system

Plant J

A golden shot: how ballistic single cell transformation boosts the molecular analysis of cereal-mildew interactions

Mol Plant Pathol

A proteomic analysis of powdery mildew (Blumeria graminis f.sp. hordei) conidiospores

Mol Plant Pathol

Analysis of a Blumeria graminis-secreted lipase reveals the importance of host epicuticular wax components for fungal adhesion and development

Mol Plant-Microbe Interact

Very-long-chain aldehydes promote in vitro prepenetration processes of Blumeria graminis in a dose- and chain length-dependent manner

New Phytol

Conserved requirement for a plant host cell protein in powdery mildew pathogenesis

Nat Genet

Naturally occurring broad-spectrum powdery mildew resistance in a central American tomato accession is caused by loss of Mlo function

Mol Plant-Microbe Interact

Calmodulin interacts with MLO protein to regulate defence against mildew in barley

Nature

Recruitment and interaction dynamics of plant penetration resistance components in a plasma membrane microdomain

Proc Natl Acad Sci USA

A regulon conserved in monocot and dicot plants defines a functional module in antifungal plant immunity

Proc Natl Acad Sci USA

mlo-based powdery mildew immunity: silver bullet or simply non-host resistance?

Mol Plant Pathol

SNARE-protein-mediated disease resistance at the plant cell wall

Nature

Tryptophan-derived metabolites are required for antifungal defense in the Arabidopsis mlo2 mutant

Plant Physiol

A glucosinolate metabolism pathway in living plant cells mediates broad-spectrum antifungal defense

Science

Two seven-transmembrane domain MILDEW RESISTANCE LOCUS O proteins cofunction in Arabidopsis root thigmomorphogenesis

Plant Cell

Conserved molecular components for pollen tube reception and fungal invasion

Science

Combined Bimolecular Fluorescence Complementation and Förster Resonance Energy Transfer reveals ternary SNARE complex formation in living plant cells

Plant Physiol

Co-option of a default secretory pathway for plant immune responses

Nature

Activity determinants and functional specialization of Arabidopsis PEN1 syntaxin in innate immunity

J Biol Chem

The multivesicular body-localized GTPase ARFA1b/1c is important for callose deposition and ROR2 syntaxin-dependent preinvasive basal defense in barley

Plant Cell